A semiconductor device includes: a substrate; a conductive line extending on the substrate in a first horizontal direction; an isolation insulating layer extending on the substrate and the conductive line in a second horizontal direction intersecting with the first horizontal direction, and defining a channel trench extending through the isolation insulating layer from an upper surface of the isolation insulating layer to a lower surface of the isolation insulating layer; a crystalline oxide semiconductor layer extending along at least a portion of an inner side surface of the channel trench and at least a portion of a bottom surface of the channel trench and coming in contact with the conductive line; and a gate electrode extending on the crystalline oxide semiconductor layer inside the channel trench in the second horizontal direction.